How to Grow Calibrachoa from Seed

Until recently, Calibrachoa was protected by patents and could not be sold as seed. But with the arrival of the Kabloom series, home gardeners can sow and grow this long-blooming, heat-tolerant, super-easy annual for containers.

Of course seed is much more economical than buying plants, but there are also other reasons to start Kabloom from seed this winter:

Germination is easy and quick

Kabloom goes from seed to bloom in about 4 months!

Seedlings will mature earlier in your home, so you can start the bloom season sooner!

So here’s how to sow and grow your Calibrachoa seed:

Drop one seed into each bio sponge of the Bio Dome, or press it lightly on top of the growing medium in a seed flat. Calibrachoa seed germinates better with light.

Place the Bio Dome or tray in a room with temperatures of about 70 to 75 degrees, or set it on a heat mat that can reach that temperature.

Look for the first shoots in one to two weeks. As soon as they emerge, give the seedlings 18 hours of light, preferably from grow lights (full-spectrum) or fluorescents. Let the seedlings rest in darkness for 8 hours at night.

Keep the soil bottom-watered, but do not fertilize until the seedlings are about a month old. Feed lightly.

When the seedlings have at least two sets of true leaves (the first set of leaves on the seedlings are really cotyledons, and will shrivel up and die in a few weeks — don’t worry!), begin watching the weather. The seedlings will be ready to transplant outdoors when all danger of frost is past and night temperatures stay above about 50 degrees.

Harden off the seedlings before transplanting outdoors. This involves bringing the whole Bio Dome, seed flat, or other container outside for just a few hours one day, then half a day the next, then a full day. Don’t skip this step; it’s important for preventing transplant shock in the young plants.

Transplant the seedlings into their permanent container and enjoy them all year long!

Kabloom will flower profusely all summer and as long into fall as the warm weather lasts. You may be tempted to collect seeds from the plants, and while they may germinate and grow, they will not look like Kabloom. The best way to propagate at home is to take cuttings of the plants in late summer, when they are still growing well and very vigorous. Here’s the best way to do that:

Cut stems from the base of the plant, right where the side stem joins the main stem.

Trim away the bottom leaves of the stem, leaving just 4 to 6 at the end.

Dip the cut stems in rooting hormone and gently plant them in moistened seed-starting soil, potting soil, or a mix of the two. Resist the urge to use garden soil for this.

Place a plastic bag loosely over the cuttings, or use the clear dome of the Bio Dome. Do not water the cuttings; you want a very humid, moist air environment so that the leaves can absorb the water they need. They have no roots yet, so watering them would rot the stems.

After a few days, look closely at the cuttings, and even give one or two an experimental tug. If you meet any resistance, the cuttings are taking root. If not, replace the dome or bag and wait another day or two. If you are concerned that the cuttings are not getting enough moisture in the air, mist them very lightly.

When they seem to be rooted, bottom-water the dome or tray, and put them under grow lights. Resume the 16 hours of light, 8 hours of darkness, 70 to 75 degree F temperature environment.

Feed them after a week or two under the lights, and continue to feed very sparingly during autumn and winter. You are essentially keeping the small plants alive until spring, when you can move them outdoors and enjoy their rapid growth and nonstop flowering all over again!

Calibrachoa is a fantastic plant for hot, humid, long-summer climates. Have fun growing Kabloom and decorating your entire landscape with its generous blooms!